High strength cobalt base alloy

ABSTRACT

COBALT BASE ALLOY CONTAINING A MINOR PORPORTION OF BERYLLIUM CHARACTERIZED BY BEING SUBSTANTIALLY FACE CENTERED CUBIC IN STRUCTURE AND HAVING INCREASED STRENGTH AND HARDNESS.

1971 R. B. HERCHENROEDER 3,598,661

HIGH STRENGTH COBALT BASE ALLOY 4 Sheets-Sheet 1 Filed Dec. 11, 1968 RC0.- Y

Pm rm mm n My Y

g- 10, 1971 R. a. HERCHENROEDER 3,598,661

HIGH STRENGTH COBALT BASE ALLOY Filed Dec. 11, 1968 4 Sheets-Sheet Z FIG.3

FIG.4

INVE TOR N ROBERT B. HERCHENROEDER e/M ATTORNEY Aug. 10, 1971 R. B. HERCHENROEDER 3,598,651

' HIGH STRENGTH COBALT BASE ALLOY Filed Dec. 11, 1968 4 Sheets-Sheet 3 FIG-.5

INVENTOR ROBERT B. HERCHENROEDER ATTORNEY Aug. 10, 1971 R. B, HERCHENROEDER 3,593,651

HIGH STRENGTH COBALT BASE ALLOY Filed Dec. 11, 1968 4 Sheets-Sheet 4 FIG.6

INVENTOR ROBERT B. HERCHENROEDER #4 4", ATTNEY United States Patent Ofiice Patented Aug. 10, 1971 US. Cl. 148-325 Claims ABSTRACT OF THE DISCLOSURE Cobalt base alloy containing a minor proportion of beryllium characterized by being substantially face centered cubic in structure and having increased strength and hardness.

This invention relates to a cobalt base alloy containing minor proportions of beryllium and having substantially increased hardness and strength. More particularly, this invention relates to a beryllium-containing cobalt base alloy essentially in the face centered cubic form having increased hardness and strength.

Cobalt base alloys are widely and effectively used at present, particularly in wear resistant applications such as bearings and seals for pumps, in particular for pumps used with molten metals. It would however be a substantial industrial benefit if a cobalt base alloy could be provided having further increased hardness together with high strength which alloy could be readily pre-formed to a desired shape, and then hardened and strengthened.

It is, therefore, an object of the present invention to provide a cobalt base alloy having increased hardness and strength.

It is another object of the present invention to provide an essentially completely face centered cubic cobalt base alloy having increased hardness and strength.

Other objects will be apparent from the following description and claims taken in conjunction with the drawing in which FIG. 1 is a photomicrograph (original magnification 20,000X) of a beryllium-containing cobalt base alloy after an initial heat treatment at 2050 F.

FIG. 2 is an electron diffraction pattern for the material of FIG. 1;

FIG. 3 is a photomicrograph (original magnification 76,000X) of the material of FIG. 1 after a second heat treatment at 1200 F., and

FIG. 4 is an electron diffraction pattern for the material of FIG. 3;

FIG. 5 is a photomicrograph (original magnification 26,000X) of a beryllium-containing cobalt base alloy which was heat treated at 2050 F. followed by a second heat treatment at 1000 F., and

FIG. 6 is an electron diffraction pattern for the material of FIG. 5.

A cobalt base alloy in accordance with the present invention contains at least about 30% cobalt and from about 0.2 to 1.3% beryllium and is characterized by a substantially completely face centered cubic matrix in which is dispersed either or both of the following:

(a) a dispersion of fine beryllium-containing precipitate, (b) a dispersion of pre-precipitation zones.

The foregoing structure is developed in the berylliumcontaining alloy by a novel heat treatment, more fully described hereinbelow, and is directly responsible for the improved hardness and strength of the alloy. In addition to beryllium, the alloy of the present invention requires the usual amount of known stabilizing elements sufficient to stabilize the face centered cubic structure of a cobalt base alloy. Such elements include iron, nickel, aluminum, manganese and zirconium. Considered individually from about 0.3 to 0.5% carbon, about 4 to 6% iron, and about 17 to 20% nickel will provide stabilization; zirconium, aluminum and manganese are generally less effective stabilizers and are used in combination with the foregoing elements. Most often a combination of stabilizing elements are used as a practical matter and in a cobalt base alloy the following aggregate amounts represent a satisfactory combination of stabilizing elements: 0.01-0.03% C.+0.1-0.3% Al+3-5% Ni+2-4% Fe+ 0.5-2.5 Mn.

In a preferred embodiment of the alloy of the present invention also contains from about 10 to 30% chromium to provide corrosion and oxidation resistance. In addition, the alloy preferably contains from 3 to 18% in the aggregate of tungsten and molybdenum for added strength by solid solution strengthening and carbide dispersion. At least about 3% nickel is required in the alloy of this invention to provide a stabilizing effect as previously mentioned and to initiate precipitation of a beryllium, i.e. beryllide, phase. The nickel content may range up to 30% to provide a partial replacement for cobalt which may be desirable for economic reasons.

Also, minor amounts of additional elements such as magnesium, silicon and calcium may be added to optimize the properties of the alloy, to deoxide the alloy, or fix the sulfur content. Also, tantalum and columbium in relatively small amounts may be added for strengthening. Effective amounts of the foregoing elements are employed to provide the noted results although it will be appreciated that the art recognizes that more than one of these elements can have multiple effects; for example zirconium has capabilities for solid solution strengthening, deoxidation and carbide forming in addition to stabilization and other known effects. In general, the aggregate of the above-noted elements magnesium, calcium, silicon, tantalum and columbium should be not more than about 5% of the alloy.

A preferred compositional range for the alloy of the present invention is about 11-13% tungsten, 0.03-0.3% carbon,18-20% nickel, 19-21% chromium, 0.4-0.9% beryllium, up to 1% Mn, up to 3% Fe, balance substantially all cobalt. This alloy composition provides exceptional strength in addition to superior hardness.

In the practice of an embodiment of the present invention, a beryllium addition of from about 0.2% to about 1.3% is made to a cobalt base alloy melt having a composition as aforedescribed and the resulting alloy is cast into an ingot. The ingot is preferably homogenized by hot working at temperatures of about 2100 F. Following homogenization, with substantially all of the alloy in the face centered cubic form, the material in a conveniently suitable shape, such as sheet, plate and bar, is heat treated to dissolve substantially all of the beryllium in the alloy in the solid solution matrix without altering, i.e. transforming the face centered cubic matrix. Heating in the range of about 2050 F. to 2150 F. for from 10-30 minutes has been found suitable with the shorter times being generally used with the higher temperatures.

Following quenching of the alloy, which is conducted at a rate such that no significant precipitation of beryllium, i.e. beryllide occurs, e.g. water quenching is suitable, the alloy is further heat treated at a lower temperature in order to produce, without any significant transformation of the matrix to the hexagonal form, either or both of the following:

(a) a dispersion of pre-precipitation zones throughout the face centered cubic matrix;

(b) a dispersion of fine beryllium-containing, i.e. beryllide, precipitate throughout the face centered cubic matrix.

A suitable temperature range for this second heat treatment is from about 900 F. to 1400 F. for from 2 to 8 hours or more. With either or both of the conditions (a) and (b) an alloy is obtained which is 95% or more in the face centered cubic form and which has substantially improved mechanical properties including improved strength and hardness.

The (a) condition noted above, i.e. pre-precipitation zones, are known to the art as Guim'er-Preston, or G-P zones, and are two dimension platelets that produce streaks on Laue X-ray photograms and electron dilfraction patterns and are pre-precipitation zones providing the initial discernible evidence of precipitation from solid solution. A publication by R. W. Fountain, G. W. Faulring and W. D. Forgeng, in the Transaction of the Metallurgical Society of AIME, vol. 221, August 1961-747, describes the procedure for the observation of such preprecipitation zones.

The condition (b) noted above is evidenced in microscopic observations as a finely dispersed phase of elongate precipitated particles having a length on the order of about several microns and less. Microscopic observations at about 25,000-75,000 will ordinarily show the presence of the dispersed beryllide precipitate.

With reference to the foregoing discussion, it is to be noted that it is not essential that a full precipitation of a beryllium phase be provided in order to obtain an alloy of improved mechanical properties, incipient precipitation as indicated by ure-precipitation zones being suflicient.

To further illustrate the present invention and with reference to the drawing, FIG. 1 shows the structure of a cobalt base beryllium containing alloy at a magnification of 20,000X which has been cast, homogenized and given an initial heat treatment at 2050 F. for minutes. The composition of this alloy is shown in Table I.

TABLE I Composition of alloy of FIG. 1

W 12.79 Ni 18.64 Cr 20.33 Be 0.55 Mn 0.66 Fe 2.15 C 0.18 S 0.012 Al 0.14

P Si 0.36 B 0.008 Co Bal.

As can be seen from FIG. 1, and FIG. 2 which is an electron diffraction pattern of the material of FIG. 1, the alloy after the solution treatment is essentially all in the face centered cubic form. Also there is no sign of any precipitation, or pre-precipitation phenomena in the alloy at this point.

FIG. 3 (76,000X) of the drawing show the structure of the alloy of Table I after a further heat treatment at 1200 F. for 4 hours. This photomicrograph shows the presence of a dispersion of fine precipitate which is indicated at 10 and represent an alloy in accordance with the present invention having increased strength and hardness.

FIG. 4 is an electron diffraction pattern of the material of FIG. 3 and shows sattellite spots which evidence the actual precipitate and elongate streaks which evidence the presence of pre-precipitation zones in a face centered cubic matrix which are present in this instance, together with an actual dispersion of fine precipitate.

With another sample of the alloy of Table I, an initial heat treatment of 15 minutes at 2050 F. was provided, followed by 16 hours at 1000 F. The photomicrograph of FIG. 5 (22,000 does not show any sign of an actual precipitate, however, the electron diffraction pattern for this material, FIG. 6, shows elongate streaks" 40 which indicate the presence of pre-precipitation zones and the existence of an alloy in accordance with the present invention having increased strength and hardness.

The following examples and data will further illustrate the present invention.

EXAMPLE I A sample of an alloy having essentially the same composition as the alloy of Table I except that its beryllium content was 0.47% was heated for 20 minutes at 2100 F. and water quenched. This alloy had a face centered cubic matrix which was free of any evidence of a beryllium containing precipitate. Hardness testing of this material gave a value of 21.9R,,.

Similar samples of the alloy were given additional heat treatment at 1100, 1200, 1300 and 1400 F. for 4, 8, 16, 24, 48 and 96 hours to develop a dispersion of precipitate and/or pre-precipitation zones. The results i]:- lustrating substantially improved hardness are shown in Table II.

TABLE IL-HARDNESS (11,) FOR 0. 47% Be ALLOY Temperature, F.

Alloy of the composition of Table I (0.55% Be) and alloy having the same composition except for beryllium (0.86% Be) were air-induction melted, cast into ingots which were forged to slabs at 2000" F., conditioned and rolled to 0.063 inch sheet and 2000 F.

Sheet samples were tested after an initial heat treatment of 15 minutes at 2000 F. followed by water quench. These samples were face centered cubic and showed no evidence of precipitate or pre-precipitation zones. Tensile data for these samples is shown in Table 111.

Additional sheet samples were further heat treated for 24 hours at 1300 F. to produce a dispersion of fine beryllium containing precipitate in the face centered cubic matrix of the alloy, and at 1000 F. for 16 hours to produce only a dispersion of pre-precipitation zones. Tensile and rupture data for these samples is shown in Tables VI, IV(a) and V. Hot hardness data is illustrated in Table VI.

TABLE IIL-TENSILE PROPERTIES OF ALLOY TREATED FOR 15 MIN. AT 2,000 F.

Yield strength, p.s.i.

TABLE IV.TENSILE PROPERTIES OF ALLOY AFTER TREATMENT AT 1300 F. FOR 24 HRS.

Yield strength, p.s.i.

Te Ultimate Percent Be temp 0.02% 0.02% strength, Elongation, in alloy F otIset offset (p.s.i.) percent 116, 829 143, 253 202, 579 18. 7 114, 517 114, 311 199, 23s 11. s 96, 445 119, 094 161, 096 14. 4 101), 718 115, 881 171, 357 1B. 4

TABLE IV(a) Be in alloy (percent) 0.55 Test temp. F.) 1000 Yield strength:

0.02% ofiset (p.s.i.) 0.2 offset (p.s.i.) 136,400 Ultimate strength (p.s.i.) 170,400 Elongation (percent) 20 TABLE V.-RUPTURE PROPERTIES OF ALLOY AFTER TREATMENT AT 1,300 F. FOR 24 HRS.

Test Reduction Percent Be in temp., Stress Lite Elongation, of area, Allo F.) (p.s.i.) (hours) percent percent 1, 200 92, 000 343. 3 7. 7 1|. 3

TABLE VI.1IOT HARDNESS DATA OF ALLOY AFTER TREATMENT AT 1,300 11. FOR 24 HRS.

Hardness (Brinell) In a further test, an alloy containing 0.02% C, 0.21% Al, 0.55% Be, 4.86% Ni, 6.25% Fe, 1.36% Mn bal. Co was forged, rolled to sheet, and heat treated for minutes at 2150" F. followed by water quench. Samples of this material which was face centered cubic without any evidence of beryllium precipitation or pre-precipitation zones exhibited an ultimate tensile strength of 100,000 p.s.i. (0.2% offset) and an elongation of 38.2%. After further heating at 1200 F. for 4 hours, the ultimate tensile strength at room temperature of the material was 136,300 p.s.i. The corresponding yield strengths were 64,600 psi. and 97,000 p.s.i. respectively.

From the foregoing, it can be seen that a novel beryllium containing cobalt base alloy has been provided which has improved hardness, 40 R and higher, and improved strength, i.e. yield strength at room temperature of higher than 100,000 p.s.i. (0.2% offset), as compared to a Co-Be alloy of the same composition, but which does not have the structure of the present invention.

6 What is claimed is: 1. A cobalt base alloy consisting essentially of about Percent Chromium 1030 Tungsten Up to 18 Molybdenum Up to 18 Nickel 4-30 Beryllium 0.2-13

balance mostly cobalt in an amount of at least with the sum of tungsten and molybdenum being in the range of about 3 to 18%, the matrix of said alloy characterized by being substantially all in the face centered cubic form and containing either or both of the following:

(a) a dispersion of fine beryllium containing precipitate,

(b) a dispersion of pre-precipitation zones. oifset tensile yield strength at room temperature of greater than 100,000 p.s.i.

3. A cobalt base alloy containing from about 0.2 to 1.3% by weight beryllium and the matrix of which is substantially all in the stable, face centered cubic form and having uniformly distributed throughout said matrix either or both of the following:

(a) a dispersion of fine beryllium containing precipitate,

(b) a dispersion of pre-precipitation zones.

4. A cobalt base alloy as in claim 3 wherein said face centered cubic form is stabilized by effective amounts of one or more elements from the group consisting of nickel, carbon, iron, zirconium, aluminum and manganese.

5. An alloy consisting essentially by weight of about:

the matrix of said alloy being substantially completely in face-centered cubic form but having uniformly distributed therethrough either or both of the following:

(a) a dispersion of fine beryllium containing precipitate,

(b) a dispersion of pre-precipitation zones.

References Cited UNITED STATES PATENTS 3,418,111 12/1968 Herchenroeder RICHARD O. DEAN, Primary Examiner US. Cl. X.R. 75l70, 171; 148-158 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3, 593 ,661 Dated August 10 1971 Robert B. Herchenroeder Inventor(s) It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In column 4, at line 63, in the fourth column of TABLE III and at line 70, in the fourth column of TABLE IV, "0.02%" (in both instances) should read "0.2%". Also, in column 4, at lines 73 and 74, the number "114,311" in the fourth column of TABLE IV should read --l4l,3ll-- and the number "161,096" in the fifth column of TABLE IV should read --161,906--.

In column 6, in the claims, claim 1 should end with the word "zones."in line 16 at room temperature of greater than 100,000 p.s.i." and insert 2. An alloy in accordance with claim 1 having a 0.2% offset tensile yield strength at room temperature of greater than 100,000 p s i Signed and sealed this 27th day of June 1972.

(SEAL) Attest:

EDWARD M. FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents Column 6, lines 17 and 18, cancel "offset tensile yield strength FORM uscoMM-oc 60376-P69 a U S, GQVEHNMENT PRINTING OFFICE l9, 0-356-33 

